// Copyright (c) 2021, gottingen group.
// All rights reserved.
// Created by liyinbin lijippy@163.com

#ifndef ABEL_FUNCTIONAL_INDIRECT_H_
#define ABEL_FUNCTIONAL_INDIRECT_H_

#include <memory>

namespace abel {

// This header defines functors for comparing and hashing pointers by pointed-to values instead of pointer addresses.
//
// Examples:
//
//  std::multiset<shared_ptr<sstring>, indirect_less<shared_ptr<sstring>>> _multiset;
//
//  std::unordered_map<shared_ptr<sstring>, bool,
//      indirect_hash<shared_ptr<sstring>>, indirect_equal_to<shared_ptr<sstring>>> _unordered_map;
//

template<typename Pointer, typename Equal = std::equal_to<typename std::pointer_traits<Pointer>::element_type>>
struct indirect_equal_to {
    Equal _eq;

    indirect_equal_to(Equal eq = Equal()) : _eq(std::move(eq)) {}

    bool operator()(const Pointer &i1, const Pointer &i2) const {
        if (bool(i1) ^ bool(i2)) {
            return false;
        }
        return !i1 || _eq(*i1, *i2);
    }
};

template<typename Pointer, typename Less = std::less<typename std::pointer_traits<Pointer>::element_type>>
struct indirect_less {
    Less _cmp;

    indirect_less(Less cmp = Less()) : _cmp(std::move(cmp)) {}

    bool operator()(const Pointer &i1, const Pointer &i2) const {
        if (i1 && i2) {
            return _cmp(*i1, *i2);
        }
        return !i1 && i2;
    }
};

template<typename Pointer, typename Hash = std::hash<typename std::pointer_traits<Pointer>::element_type>>
struct indirect_hash {
    Hash _h;

    indirect_hash(Hash h = Hash()) : _h(std::move(h)) {}

    size_t operator()(const Pointer &p) const {
        if (p) {
            return _h(*p);
        }
        return 0;
    }
};

}  // namespace abel

#endif  // ABEL_FUNCTIONAL_INDIRECT_H_
